The proposed research project involves the application of our new method for the measurement of oxygen concentration profiles in living animal tissues and cells. This technique is based on the observation that the fluorescence emission of pyrenebutyric acid is quantitatively quenched by oxygen. Thus, by monitoring either the fluorescence intensities or lifetimes of pyrenebutyric acid which is administered to biological samples by injection, topical application or in microcapsules, the local concentration of oxygen can be determined. Both the spatial and temporal variations of oxygen concentration can be monitored permitting the resolution of the questions regarding the transport and utilization sites for oxygen in living systems. The specific objectives of this project include: (1) The simultaneous determination of microregional blood flow and oxygen tension to elucidate the mechanism of cerebral oxygen homeostasis in the face of hypoxia, ischemia and cerebral activity. (2) The construction of oxygen sensitive membranes suitable for clinical application. (3) Studies on intracellular oxygen distribution to test the hypothesis that oxygen is localized along the endoplasmic reticulum x mitochondrium x peroxisome axis and excluded from the cytosol.